In U.S. Pat. No. 3,435,744 there has been described an automatic focusing system in which the distance of an object from the camera is determined by training a beam of light upon such object and receiving reflections of that beam on a photocell which is laterally offset from the location of the beam source, the photocell being part of an ancillary optical system which is angularly oscillatable in a scanning sweep to let its own axis intersect the beam axis at different distances from the camera objective. The optical system is mechanically linked with a device for focusing the camera objective by axially displacing one of its lens members.
U.S. Pat. No. 3,838,275 describes a photoelectric comparator designed to determine a coincidence between two projected images produced by respective branches of a range finder, the comparator comprising two arrays of photocells each illuminated by discrete image portions. When the two cell arrays have identical outputs, the projected images are presumed to register with each other. A similar system is described in U.S. Pat. No. 3,844,658.